waves chapters 10 & 12. the nature of waves chapter 10 sections 1 & 2

WavesWaves

Chapters 10 & 12Chapters 10 & 12

The Nature of WavesThe Nature of Waves

Chapter 10 Sections 1 & 2Chapter 10 Sections 1 & 2

What is a wave?What is a wave?

• Def:Def: a repeating movement that transfers a repeating movement that transfers energy through matterenergy through matter

• Types of waves:Types of waves:• TransverseTransverse: matter (up/down) moves at right : matter (up/down) moves at right

angles with the wave (left/right)angles with the wave (left/right)

Other TypesOther Types

• Compressional:Compressional: matter moves in the matter moves in the same direction as wavesame direction as wave

Parts of a Transverse WaveParts of a Transverse Wave

Parts of a Compressional Parts of a Compressional WaveWave

Wave PropertiesWave Properties

• Wavelength:Wavelength: distance between one distance between one point on a wave an the next just like point on a wave an the next just like itit

Wave PropertiesWave Properties

• Frequency:Frequency: number of wavelengths number of wavelengths that pass a fixed point each secondthat pass a fixed point each second

• Count the # of crests or the # of Count the # of crests or the # of compressionscompressions

• Unit: Hertz (Hz) = 1/s = sUnit: Hertz (Hz) = 1/s = s-1-1

• Period:Period: amount of time it takes one amount of time it takes one wavelength to pass Unit: secondwavelength to pass Unit: second

Wavelength vs. FrequencyWavelength vs. Frequency

• Long wavelength = low frequencyLong wavelength = low frequency

• Inversely related: one is up the other Inversely related: one is up the other is downis down

Wave SpeedWave Speed

• Depends on the medium it is Depends on the medium it is traveling throughtraveling through

• Sounds: faster in liquids and solids or Sounds: faster in liquids and solids or warmer airwarmer air

• Light: slower in liquids and solidsLight: slower in liquids and solids

Calculating Wave SpeedCalculating Wave Speed

speed(m/speed(m/s)=frequency(Hz)xwavelength(m)s)=frequency(Hz)xwavelength(m)

c = c = v v

CalculationsCalculations

• A wave has a frequency of 500.0 Hz A wave has a frequency of 500.0 Hz and a wavelength of 3.0m. What is and a wavelength of 3.0m. What is the speed of wave?the speed of wave?

• What is the wavelength of a wave What is the wavelength of a wave that has a frequency of 20.0 Hz and that has a frequency of 20.0 Hz and a speed of 340 m/s?a speed of 340 m/s?

Amplitude and EnergyAmplitude and Energy

• Amplitude:Amplitude: related to the energy related to the energy carried by the wavecarried by the wave

• High amplitude = High energyHigh amplitude = High energy

Amplitude and EnergyAmplitude and Energy

• Compressional Amplitude Compressional Amplitude denser denser the compressions = higher amplitudethe compressions = higher amplitude

The Behavior of WavesThe Behavior of Waves

Chapter 10 Section 3Chapter 10 Section 3

ReflectionReflection

• A wave strikes an object and A wave strikes an object and bounces backbounces back

• All waves can reflectAll waves can reflect

• Echoes – sounds wavesEchoes – sounds waves

reflectingreflecting

Law of ReflectionLaw of Reflection

• Incidence beam Incidence beam and reflected beamand reflected beam

• Normal line – Normal line – perpendicular to perpendicular to mirrormirror

• Def:Def: angle of iangle of i and and angle of rangle of r are are equalequal

RefractionRefraction

• Light travels at Light travels at different speeds in different speeds in different mediumsdifferent mediums

• Change speed – Change speed – change anglechange angle

• Def:Def: bending of a bending of a wave caused by wave caused by change in speed change in speed from one medium from one medium to anotherto another


• Slower Slower in water – in water – bends towardsbends towards normalnormal

• FasterFaster in air – in air – bends awaybends away from from normalnormal


• Objects in water Objects in water are are fartherfarther than than they appear!they appear!

DiffractionDiffraction

• Def:Def: object causes a wave to change object causes a wave to change direction and bend around itdirection and bend around it

• Diffraction – around an objectDiffraction – around an object

• Refraction – through an objectRefraction – through an object

How much Diffraction?How much Diffraction?

• Obstacle smaller than wavelength – waves Obstacle smaller than wavelength – waves bendbend

• Obstacle larger than wavelength – waves Obstacle larger than wavelength – waves not affected muchnot affected much

• Hear sounds from room before see light Hear sounds from room before see light from roomfrom room

• Sound waves close to size of door – bend Sound waves close to size of door – bend around dooraround door

• Light – too small doesn’t diffract and bendLight – too small doesn’t diffract and bend

Diffraction of Radio WavesDiffraction of Radio Waves

• AM – longer waves – diffracted much AM – longer waves – diffracted much easier – travel farther distanceseasier – travel farther distances

• FM – smaller waves – aren’t affected FM – smaller waves – aren’t affected as much – don’t go as faras much – don’t go as far

InterferenceInterference

• Def:Def: when two or more waves combine when two or more waves combine and form a new waveand form a new wave

Constructive InterferenceConstructive Interference

• Waves ADD together – crests arrive at Waves ADD together – crests arrive at same place at same timesame place at same time

• Amplitude = sum of twoAmplitude = sum of two

Destructive InterferenceDestructive Interference

• Waves SUBTRACT each other – one crest Waves SUBTRACT each other – one crest meets with one troughmeets with one trough

• Amplitude – difference of twoAmplitude – difference of two

Standing WavesStanding Waves

• Def:Def: wave pattern when waves of wave pattern when waves of same wavelength and amplitude same wavelength and amplitude meet from opposite directionsmeet from opposite directions

• Crest/Crest = amplitude Crest/Crest = amplitude Crest/Trough = nodeCrest/Trough = node

• Wave “stands still” because it Wave “stands still” because it appears to not move - vibratesappears to not move - vibrates

ResonanceResonance

• Objects have own natural frequenciesObjects have own natural frequencies

• Depends on size, shape, material, etc.Depends on size, shape, material, etc.

• Def:Def: object is made to vibrate by object is made to vibrate by absorbing at its natural frequencyabsorbing at its natural frequency

• Object absorbs more energy – higher Object absorbs more energy – higher amplitude – could break apartamplitude – could break apart

• Tacoma Narrows BridgeTacoma Narrows Bridge


Electromagnetic SpectrumElectromagnetic Spectrum

What are Electromagnetic (EM) What are Electromagnetic (EM) Waves?Waves?

• Def: Def: vibrating electric charges and vibrating electric charges and can travel through space with no can travel through space with no mattermatter

Range of FrequenciesRange of Frequencies

• EM waves have WIDE range of EM waves have WIDE range of frequenciesfrequencies

• The range = Electromagnetic SpectrumThe range = Electromagnetic Spectrum

Radio WavesRadio Waves

• All around you – can’t see or hear All around you – can’t see or hear themthem

• Sound = compressional waveSound = compressional wave

• Radio = transverseRadio = transverse

• Radio:Radio: wavelengths 1 mm or longer wavelengths 1 mm or longer

Microwaves – Type of Radio Microwaves – Type of Radio WaveWave• Def:Def: wavelengths less than 1m wavelengths less than 1m• Wavelengths of 1cm – 10cm used for cell phones Wavelengths of 1cm – 10cm used for cell phones

and satellitesand satellites• Microwave ovens?Microwave ovens?• Vibrate water molecules – friction = thermal energyVibrate water molecules – friction = thermal energy

RadarRadar

• RaRadio dio ddetecting etecting aand nd rranginganging

• Send radio wave and measure how Send radio wave and measure how long it takes to bounce back – long it takes to bounce back – location is found location is found

Magnetic Resonance Imaging Magnetic Resonance Imaging (MRI)(MRI)• Developed in 1980sDeveloped in 1980s• Cylinder – powerful magnet, radio wave emitter and detectorCylinder – powerful magnet, radio wave emitter and detector• pp++ in H atom align to magnet in H atom align to magnet• Radio waves cause pRadio waves cause p++ to flip to flip• Flipping releases radiant energyFlipping releases radiant energy• Radio detector reads energy – maps your insidesRadio detector reads energy – maps your insides

Infrared WavesInfrared Waves

• Warmth – transmitted by IR wavesWarmth – transmitted by IR waves

• Def:Def: wavelengths 1mm – 750 wavelengths 1mm – 750 billionths of meterbillionths of meter

• Remotes for TVs – computers reading Remotes for TVs – computers reading CD-ROMSCD-ROMS

• Hotter objects – shorter wavelengths Hotter objects – shorter wavelengths – IR imaging– IR imaging

Visible LightVisible Light

• ROY G BIVROY G BIV• Only form can detect with eyes (rods Only form can detect with eyes (rods

and cones)and cones)• Def:Def: wavelengths 750 billionths to 400 wavelengths 750 billionths to 400

billionths of meterbillionths of meter• Eyes pick up different wavelengths = Eyes pick up different wavelengths =

colorcolor• Red – long waveRed – long wave• Violet – short waveViolet – short wave

Ultraviolet WavesUltraviolet Waves

• Def:Def: wavelengths 400 billionths to 10 wavelengths 400 billionths to 10 billionths of a meterbillionths of a meter

• Bad = enter skin cells = wrinkles or Bad = enter skin cells = wrinkles or cancercancer

• UVA – longer waves than UVB (sunburn)UVA – longer waves than UVB (sunburn)

• Good = allows body to make vitamin DGood = allows body to make vitamin D

• Good = kills bacteria – damage cells = Good = kills bacteria – damage cells = deathdeath

Ozone LayerOzone Layer

• Ozone = OOzone = O33

• Constantly formed Constantly formed and destroyed by and destroyed by UV wavesUV waves

• Destroyed by CFCs Destroyed by CFCs – 1 Chlorine atom – 1 Chlorine atom can destroy can destroy thousands of Othousands of O33

X-rays and Gamma RaysX-rays and Gamma Rays

• Smallest wavelengths highest frequenciesSmallest wavelengths highest frequencies• X-raysX-rays: wavelengths of 10 billionths to ten : wavelengths of 10 billionths to ten

trillionths of a metertrillionths of a meter• Images of bones, bags in airportImages of bones, bags in airport• Gamma Rays:Gamma Rays: wavelengths shorter than wavelengths shorter than

10 trillionths of a meter10 trillionths of a meter• Produced in nuclei of atomsProduced in nuclei of atoms• X-rays and Gamma Rays used in radiation X-rays and Gamma Rays used in radiation

therapy – kill healthy and diseased cellstherapy – kill healthy and diseased cells


Radio CommunicationRadio Communication

Radio TransmissionRadio Transmission

• Radio waves vibrate eRadio waves vibrate e-- in radio in radio antenna.antenna.

• EE-- produce electric current carries info produce electric current carries info

• Amplifier boost current and sends to Amplifier boost current and sends to speakers to vibrate speakers to vibrate ears ears brain brain

• Each station = certain frequency = Each station = certain frequency = carrier wavecarrier wave

• Carrier wave is modified to send infoCarrier wave is modified to send info

AM radioAM radio

• AM varies the AM varies the amplitude of amplitude of carrier wave – carrier wave – AAmplitude mplitude MModulationodulation

• Changing amp – Changing amp – speakers vibratespeakers vibrate

• 540,000 – 540,000 – 1,600,000 Hz1,600,000 Hz

• Measured in kHzMeasured in kHz

FM RadioFM Radio

• FM varies the FM varies the frequency of carrier frequency of carrier wave – wave – FFrequency requency MModulationodulation

• Strength is constant Strength is constant = clearer sound= clearer sound

• 88 mil – 108 mil88 mil – 108 mil

• Measured in MHzMeasured in MHz

Frequency UsageFrequency Usage

TelevisionTelevision

• Radio and TV both use carrier wavesRadio and TV both use carrier waves

• Audio – FM signal Pics – AM signalAudio – FM signal Pics – AM signal

• Pictures formed by Pictures formed by cathode-ray cathode-ray tubetube – sealed vacuumed tube with 1 – sealed vacuumed tube with 1 or more beams of eor more beams of e-- produced produced

• Color TV – 3 beams of eColor TV – 3 beams of e-- directed at directed at screen with magnetic fieldscreen with magnetic field

TelevisionTelevision

• Screen has over 100,000 rectangular spots that Screen has over 100,000 rectangular spots that glow red, green or blue when struckglow red, green or blue when struck

• Makes image when 3 beams sweep over screen Makes image when 3 beams sweep over screen – control color and brightness of each spot– control color and brightness of each spot

TelephonesTelephones

• Sound waves in microphone Sound waves in microphone electrical signal (radio wave)electrical signal (radio wave) microwave towermicrowave tower

• Cell phoneCell phone uses one signal to send uses one signal to send info another signal to receiveinfo another signal to receive

• Each base covers cell – move from Each base covers cell – move from cell to cell – automatically transfers cell to cell – automatically transfers signalsignal

Cordless PhonesCordless Phones

• TransceiverTransceiver – transmits one signal – transmits one signal and receives another from a base and receives another from a base unitunit

• Using dif frequencies allows you to Using dif frequencies allows you to talk and listen at the same timetalk and listen at the same time

SatellitesSatellites

• Satellite Telephones – can make calls Satellite Telephones – can make calls over the worldover the world

• Phone – satellite – ground station – Phone – satellite – ground station – phonephone

• Long delaysLong delays• Satellite TV – high frequency Satellite TV – high frequency

microwaves rather than radio wavesmicrowaves rather than radio waves• Why are dishes curved?Why are dishes curved?• To direct waves to antennaTo direct waves to antenna

Global Positioning System Global Positioning System (GPS)(GPS)

• Def:Def: satellites, ground stations, and satellites, ground stations, and receivers give your exact locationreceivers give your exact location

• Satellites owned by US Dept. of Satellites owned by US Dept. of Defense – signals used by anyoneDefense – signals used by anyone

waves chapters 10 & 12. the nature of waves chapter 10 sections 1 & 2

Documents